The present invention generally relates to electrical connecting methods, and more particularly to an electrical connecting method which makes an electrical connection using a gallium (Ga) system liquid metal. Note that, as per convention, a Ga system identifies a system that has Ga as its primary component.
Recently, the number of terminals has increased and the pitch of the terminals has become narrower due to the reduced size of electronic devices and the high packaging density. For this reason, how to detachably connect a large number of terminals extending from a large scale semiconductor integrated circuit device, a printed circuit and the like is becoming an important problem to be solved.
Conventionally, connectors are used to detachable connect the terminals. The connector has various shapes and configurations depending on the object and use of the connection. But basically, the connector is made up of a plurality of plugs and a plurality of receptacles. Each plug is inserted into the corresponding receptacle and is held thereby to make the electrical connection.
In the normal connector, the connection and disconnection can be made manually if the number of terminals to be connected is on the order of approximately 100. If the inserting force required per terminal is 100 gf, for example, it requires an inserting force of 10 kgf to connect 100 terminals.
But in the printed circuit having a large number of large scale semiconductor integrated circuit devices mounted thereon, the number of terminals to be connected is on the order of several hundred to several thousand. In this case, the connector cannot be connected and disconnected manually. For this reason, methods such as the so-called low inserting force (LIF) method or the zero inserting force (ZIF) method is employed to facilitate the connection and disconnection of the connector. According to such methods, the contact part of the receptacle opens to facilitate insertion and extraction of the corresponding plug. However, the mechanism required to carry out such methods is complex and is unsuited for application to small electronic devices.
On the other hand, methods using a liquid metal have been proposed to make the electrical connection. For example, a metal which is liquid under room temperature is used for the receptacle, and the plug is inserted into the liquid metal receptacle or, at least one of the two contacts to be connected is coated with a liquid metal before the two contacts are connected. However, the methods using the liquid metal have yet to solve the problems which will be described hereunder.
The most familiar metal which is liquid under room temperature is probably mercury (Hg). For example, a method using Hg in a contact part of the connector is proposed in a Japanese Laid-Open Patent Application No.57-123673. Hg may not have been used for the connector, but it was well known to use Hg for a small number of terminals of experimental devices. However, although Hg is toxic, it is difficult to use Hg in a perfectly sealed environment and the use of Hg in the connector having a large number of terminals is impractical for safety reasons.
On the other hand, it is conceivable to use an eutectic alloy of Ga such as gallium-indium (Ga--In) and gallium-tin (Ga--Sn) which has an extremely low melting point and is liquid under room temperature. The use of Ga--In is proposed in a Japanese Laid-Open Patent Application No. 58-130540, for example. It is convenient to use such an eutectic alloy of Ga for the electrical connection because the melting point of the eutectic alloy can be varied depending on the composition. For example, it is possible to set the melting point of the eutectic alloy so that the temperature rises and the eutectic alloy is melted during operation of the device, and the eutectic alloy is solid while the device is stopped so as to facilitate moving of the device.
Therefore, the use of the eutectic alloy of Ga in the connector is advantageous in that the connection and disconnection can be made without the need of large inserting and extracting forces. However, the easy corrosion of this eutectic alloy makes it difficult to apply the connecting method to an open system.